From what i found with my phone, I would like to confirm that even if phone is turned off, power is still supplied to few wires.
When i remove battery from my phone and then put it back and turn it on, it would ask me to configure date settings. But if I just turn the phone off and then turn it on, it doesn't prompt me to configure date settings. so I can tell that at least the clock on my phone uses battery even when the phone is turned off.